In drilling, completion or service operations in a deviated well, it is sometimes important to be able to seal the tubing string to isolate production or other pressurized zones of the wellbore.
In the past, tubing end-plugs have been used during injection of tubing into such a well, the plugs generally being a metallic or aluminum disc attached to the bottom of the tubing string prior to injection, and then the removal of the metallic disc from the tubing string at or near bottom hole. An example is found in U.S. Pat. No. 244,042 Farrar (1881). This has the undesirable effect of leaving the metal at the bottom workface of the wellbore which is difficult or expensive to remove and can interfere with further drilling or other operations. These devices have only been run at the bottom of a tubing string.
Another mechanism sometimes seen is the use of an Otis® nipple, consisting of multiple profiles to receive a variety of plug devices via wireline delivery downhole. These mechanisms provide for a single plug, and while unpluggable and repluggable, are constrained by the plug delivery mechanism—that is, wireline plugs may be difficult to retrieve from deep deviated or horizontal wellbores, and may be impossible to inject and refit in non-vertical orientations. Additionally, if such a plug fitting fails during operations, the wireline plug may become a projectile, and two wireline plugs cannot or cannot easily be installed during or for operations. Similarly, multi-profile landing nipples to receive a variety of plugs are manufactured under the Baker® trade name.
Rupture domes have been used in similar situations downhole. For instance, a system providing a “Frangible Pressure Seal” is disclosed in Canadian Patent Application 2,228,728 by Frazier (CA'728). In that case ceramic shells with a circular seating face and a radial curvature are provided as a breakable seal for inclusion in a downhole subassembly. In CA'728, the ceramic disc is formed with a precise arcuate shape (in cross-section) to offer maximum pressure resistance. CA'728 is designed to provide a strong barrier to fluid pressures, yet be capable of being broken by wielding a breaking implement downhole (such as by dropping a bar down the tubing). This design would be unsuitable, for instance, in a deviated or non-vertical well-bore's tubing string because the bar or breaking implement could not be propelled by gravity alone should the non-vertical portion of the wellbore be a very great distance, or should the curvature of the deviated bore impair the breaking tool's travel velocity (or striking force). Additionally, where the domes of '728 are ruptured, the resulting passage may be irregular and restrict fluid flow in the tubing's bore past the remnants of the dome. As well, resulting fragments may be irregular or large which may interfere with fittings, drilling, or other well bore characteristics or operations.